Electrolyte Thermodynamic Models in Aspen Process Simulators and Their Applications

Abstract

Electrolyte systems are becoming increasingly important as the process industries transition to better address environmental sustainability and climate change. Industrial processes such as carbon capture and sequestration, brine water treatment, lithium refining, and many others require accurate and rigorous electrolyte thermodynamic models to support process simulation and design of chemical processes involving electrolyte systems. Distinctly different from nonelectrolyte systems, the solution nonideality of electrolyte systems is primarily characterized by the electrolyte solution chemistry and secondly impacted by the subsequent physical interactions and associations of true species in solutions. This Article presents the methodology in Aspen process simulators to address the solution chemistry with true species and apparent component approaches together with the two electrolyte thermodynamic models, Pitzer and Electrolyte Nonrandom Two-Liquid equations. Also covered are experimental data compilation, best practice in data regression, and industrial applications highlighted with CO 2 capture with amine solutions and high salinity brine solutions. We further present our perspectives in current challenges and emerging opportunities with thermodynamic modeling for electrolyte systems with high charge density ions, transport property estimation, and systematic data collection and verification.

Current Practices and Continuing Needs in Thermophysical Properties for the Chemical Industry

“…234 Also, Thomsen provides a useful practical guide/tutorial for electrolyte activity coefficient models. 253 In the context of industrial simulations, the most widely used models are the Pitzer molality-based model 252 and electrolyte NRTL model of Chen and coworkers, 75 extended UNIQUAC model of Thomsen et al 254 and MSE model of Wang et al 81 In the special issue, Wang et al 111 reviewed the use of electrolyte thermodynamics (as exemplified by the Pitzer and electrolyte NRTL models) within the Aspen-Plus process simulation environment. In another companion article, Yang et al 68 Recent progress in activity coefficient models includes the explicit treatment of association and solvation based on the Wertheim theory, 46,255 This approach extends the previously used solvation concepts 256 using the activity coefficient version of Wertheim theory that has shown promise for a variety of associating non-electrolyte systems.…”

“…47 Original studies in this area were carried out by Bansal 257 using molecular dynamics simulations. As pointed out by Wang et al 111 high density cations exhibit a strong hydration tendency with electron donor sites of the solvent water molecules and a strong ionpairing tendency with anions as strong electron donors and this approach is able to account for both of these interactions at the same time. Inability to model this hydration behavior correctly is a major limitation of the current models in chemical engineering practice.…”

“…Similarly, the density is obtained by differentiation with respect to pressure. This methodology has been used to develop highly accurate reference models for aqueous solutions of individual common salts such as NaCl and KCl. , As described by Wang et al of OLI Systems and Wang et al of Aspen Technologies, the same methodology can be used in conjunction with a general-purpose engineering electrolyte Gibbs energy model to calculate the enthalpy, heat capacity and density of multicomponent electrolyte systems. However, it should be noted that this approach typically requires careful parametrization of the master Gibbs energy model using sufficiently extensive multiproperty data and is best implemented in comprehensive, speciation-dependent codes for electrolyte systems.…”

“…A similar approach has been shown to represent thermal conductivity of aqueous and mixed-solvent electrolyte systems . Approaches of Wang et al are also similar . These semiempirical approaches require a limited number of adjustable parameters and are applicable to multicomponent systems.…”

“…63 Articles by Lira et al, 46 Lira et al, 48 Fouad et al, 64 and Elliott 65 describe recent developments regarding Wertheim association theory. These are followed by articles on multisolvent electrolytes phase equilibrium by Wang et al, 111 Djamali, 67 and Yang et al, 68 physical property models for adsorption and nanopore, 69,70 molecular simulations for bioseparations, 66 mesoscale modeling of micellization and adsorption of surfactants, 71 use of micelle formation for bioseparations, 72 and non-electrolyte product properties. 73…”